U.S. Pat. No. 6,375,170 discloses a spring system having first and second spring units mounted in mirror image to each other. Each of the two spring units comprises essentially a flexible member and a roll-off piston. An outer jacket common to both spring units is provided for lateral limiting and as a counter support to the two roll-off pistons. The flexible members likewise roll off on the outer jacket. The two flexible members can form a single piece. The roll-off pistons are slightly conically configured at the ends and the outer jacket is configured conically at both ends. The annular gap between the roll-off pistons and the outer jacket is open so that there is no protection against dust. For this reason, the problem of the sensitive flexible member roll-off surfaces being subjected to dirt and contaminants is present. The reliability is no longer ensured when the flexible member becomes dirty. Accordingly, the expected service life is drastically reduced.
German patent publication 100 24 572 discloses a combined spring damper system having a double flexible member. This system includes two roll-off pistons mounted axially opposite to each other and on which corresponding tubular-shaped flexible members can roll off. Each of the tubular-shaped flexible members is connected, on the one hand, to a roll-off piston and, on the other hand, to each other via a connecting sleeve.
German patent publication 199 13 754 discloses a spring element for an air spring system. The spring element is configured of an inner tube-shaped first flexible member and an outer second flexible member which is essentially the same geometrically as the first flexible member. The first flexible member is made of weaker material and this material is more readily deformable. The second flexible member functions as the outer guide for the first flexible member.
It is an object of the invention to provide a spring system which provides a longer service life with simple constructive means.
The spring system of the invention includes: first and second spring units mounted coaxially to each other; the first spring unit including a first roll-off piston and a first rolling-lobe flexible member coacting with the first roll-off piston during operation of the spring system; the second spring unit including a second roll-off piston and a second rolling-lobe flexible member coacting with the second roll-off piston during operation of the spring system; the first and second roll-off pistons being rigidly connected to each other to define a double roll-off piston; an outer jacket common to both of the first and second spring units; the first and second rolling-lobe flexible members and the double roll-off piston conjointly defining a common pressure space filled with a fluid; a contamination flexible member connected between the double roll-off piston and the outer jacket; and, the contamination flexible member having an effective length shorter than the shorter of the first and second rolling-lobe flexible members so that the contamination flexible member functions as a stop during the operation of the spring system.
With the invention, a contamination of the inner-lying components and especially a contamination of the flexible member roll-off surfaces is prevented. This is achieved with a contamination flexible member arranged in accordance with the invention between one of the roll-off pistons and the outer jacket.
The contamination flexible member is clamped, on the one hand, in the region of a roll-off piston and, on the other hand, on the outer jacket. The effective length of this contamination flexible member is somewhat less than the effective length of the shorter of the two working flexible members. In this way, the contamination flexible member functions also as an end stop (pull stop). The fact that there is a slightly shorter maximum stroke (spring path) is of no consequence.
With the use of clamp rings and adapters coacting with the clamp rings, an air-tight contact engagement of the flexible member on the roll-off piston and on the outer jacket is achieved. The air-tight contact engagement effectively prevents a relative slippage when applying a pull or push force on the flexible member.
With a targeted arrangement of a reinforcement layer arranged within the contamination flexible member, the pull stop characteristic line can be influenced. The reinforcement layer comprising reinforcement cords can, for example, be arranged in the fabric or material of the contamination flexible member, for example, in a range of 0xc2x0 to 90xc2x0 to the axial direction. The contamination flexible member functions as an end stop and takes up static forces (for example, those forces which occur with jacking up of the vehicle) as well as dynamic forces during excessive spring deflection. In this way, the flexible member combines the characteristics of two components in one in an advantageous manner, namely: end stop and a protection against contamination.
To prevent the situation that the contamination flexible member becomes creased or crushed during spring compression, this flexible member is so configured that it rolls off by itself under atmospheric pressure. A slight inner overpressure is provided to support the roll-off operation as needed. For this purpose, the contamination flexible member can be provided with a pressure-limiting valve or an overpressure flap.
The flexible member according to the invention is especially provided for the use in motor vehicle air springs or hydraulic springs (medium is air or oil). Other applications are in uses for driver seat air springs, driver cabin air springs and industrial support air springs.